Plastic pyrotechnic compound



United States Patent 2,984,558 PLASTIC PYROTECHNIC COMPOUND EdwardRolle, San Diego, and John Q. Tabor, Jr., Los Angeles, Calif., assignorsto the United States of America as represented by the Secretary of theNavy The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The present invention relates in general to a pyrotechnic material therate of combustion of which may be accurately predetermined. Moreparticularly, the invention is directed to a relatively slow-burningplastic compound which may readily be cast or molded at roomtemperatures without the application of external pressure.

It is customary to manufacture certain types of combustible articles,such for example as flares, safety fuses, and the-like, byfilling ahollow tube or container with the combustible mixture in powder form (towhich a binder may or may not be added) and then subjecting the mixtureto a pressure as high as several thousand pounds per' square'inch. Theresulting product has a density dependent upon its composition, upon thedegree of moisture present, and upon the amount and duration of thepressure thus applied. The nature of these factors makes them somewhatdiflicult to accurately control, especially insofar as the degree ofambient humidity is concerned. Hence, pyrotechnic articles fabricated bysuch a process show quite wide variations in their rate of combustion.

Such variations in burning rate cannot be tolerated in many situationswhere the article so made is employed as'a-fuse 'or timing device, or inthe testing of guided missiles or rockets, where specific data as to theperformance of the'missile'is extremely important in dictating possibledesign changes or modifications. Under such conditions, the missile tobe tested may have attached thereto a flare of-high luminosity whichpermits the missile to be tracked by visual and/or photographic methods.The flare is ignited when the missile is launched, and continues 'toburn for a time sufficient to provide the missile position data desired.v.To ensure constant burning at'highaltitudes, as well as reliableignition at low temperatures, high luminosity, and maximum compactness,the flare is so constructed as to be ignited by exposing the surface ofthe illuminant to a flame generated by an electrical discharge in asquib filled with some such material as black powder. The squib is heldin proximity to the flare illuminant by a protective cap, customarilymade of a fusible material which partially melts when the illuminant isfully ignited, at which time both the cap and the squib are ejected andthe flare begins to burn at full luminosity as the missile is launched.It is essential that the flare material be fully ignited at the instantof launching, as otherwise tracking during the initial period of missileflight is hampered. On the other hand, ignition obviously should notbegin prematurely. It is highly desirable that the squib flame bechanneled over the entire surface of the material to be ignited, andthat the squib and cap are not ejected before ignition is complete.

, Patented May 16, 1961 While the arrangement set forth above has provengenerally satisfactory in practice, the desirability of finding a way toeliminate the fusible flare cap has been recognized. This is due inlarge part to the fact that this protective cap is ejected in anunpredictable direction at the instant of missile launching, andconstitutes a hazard to the launching aircraft. One solution has been toconstruct the cap of a material which melts completely, such as Rosesalloy, or of a material such as nitrocellulose which is adapted to burnwhen the flare illuminant is ignited. Such expedients are disclosed in aco-pending United States patent application of Thomas H. Johnson, ErnestM. Kane, and John Q. Tabor, Serial No. 603,458, filed August 10, 1956,Patent No. 2,868,129, and entitled Flare Device. A further possibilitylies in the design of a pyrotechnic member in which both the flare bodyand cap are formed as a unit from the same consumable material, thusdispensing not only with the separate cap, but also with the hollow tubeor container in which the combustible substance is customarily packed.

It is apparent that, in either of the above arrangements, the rate ofburning of the consumable material is of great importance. If this rateis constant, then a moment may be chosen for electrical energization ofthe squib which willproduce full illumination of the flare at theinstant of missile launching regardless of the ambient temperature.Previously used pyrotechnic materials, as above brought out, are subjectto such wide variations in density that the actual burning rate may beconsiderably higher or lower than that relied upon, thus causing eithera delayed or, a premature ignition of the flare.

To eliminate such a condition in the above as well as otherapplications, the present invention provides a combustible plasticsubstance which may be readily cast or molded at room temperatureswithout the necessity of supplying external pressure, and which, whenhardened, is unusually resistant both to moisture and to'wide variationsin temperature. Furthermore, the material of the present invention is ofuniform density throughout, and exhibits an-essentially constant burningrate which may be accurately pretermined or controlled by varying therelative proportions of its constituents. Thus it is admirably suitedfor use as a pyrotechnic compound which may be cast or molded in theform of a flare, for example, having neither an outer casing nor aseparate cap for holding the igniting means. 7

One object of the present invention, therefore, is to provide animproved pyrotechnic material which may readily be cast or molded atroom temperatures without the application of either heat or pressure,and which will harden without developing cracks or fissures.

Another object of the present invention is to provide an improvedpyrotechnic material which has an essentially constant rate of burning,which rate may be accurately predetermined or'precalculated inaccordancewith the relative proportions of its basic constituents.

A further object of the invention is to provide a pyrotechnic materialparticularly adapted for use in flares of the type employed in thetesting of guided missiles or rockets.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description.

The combustible material of the present invention consists essentiallyof a mixture of unsaturated polyester resins, to which is added astabilizing ingredient, oxidizers, and a fuel which has (at least inpart) been comminuted or atomized to a fineness of approximately 325mesh. As an example, a composition of the following ingredients, withinthe respective ranges set forth, has proven highly satisfactory as apyrotechnic material which hardens without cracking or fissuring at roomtemperatures and without the application of external pressure. Themixture consists of equal amounts by weight of a resinous compound and afuel, made up according to the following table:

Resin-nus compound Resin A is an unsaturated polyester resin havingstyrene as a reactive monomer, and is derived from propylene glycol,maleic anhydride and phthalic anhydride, the ratio of maleic anhydrideto phthalic anhydride being relatively high. One preferred example ofResin A is marketed commercially under the trade name Laminac Resin#4128.

Resin B is an unsaturated polyester resin having styrene as a reactivemonomer, and is of the flexible type based upon diethylene glycol,maleic anhydride and adipic acid. One preferred example of Resin B ismarketed commercially under the trade name Laminac Resin #4134."

The methyl ethyl ketone peroxide may be 60% in 40 dimethyl phthalatemixture or 40% dioctyl phthalate.

Fuel

Parts Magnesium powder (70% through 325 mesh) 1 Potassium or ammoniumperchlorate, KCIO; or

NH ClO (as an oxidizer) 2 The resinous compound when prepared is viscousin character. The fuel is added slowly to this resinous compound whilethe latter is agitated by some means such as a mechanical stirrer. Whenthoroughly mixed the material is poured into molds and allowed to hardenat room temperature. The time required for this hardening process willof course depend upon the size and shape of the product, and if it isnecessary to shorten this hardening period the mold may be heated, as inan electric oven, at a temperature which does not exceed approximately180 Fahrenheit. When allowed to harden naturally, the slow rate ofpolymerization yields a pyrotechnic article which is unusually free fromthe cracks and/or other molding defects frequently found in pressedproducts.

The following table illustrates one particular resinous compound whichhas been employed satisfactorily in the invention mixture:

Ingredient Percent by weight Resin A 56 Resin B 34 Benzyl Alcohol 4Cobalt Napthenate 2 Methyl Ethyl Ketone Peroxide 4 It will now beappreciated that a pyrotechnic mixture formulated in accordance with thepresent disclosure requires no complex vacuum or pressure equipment, andutilizes no oven or other heater if time permits normal hardening. Onlyinexpensive molds are employed in conjunction with a readily obtainablestirrer or other mixing apparatus, and hence the heavy and cumbersomecompression loading equipment, used in conventional manufacturingprocesses, is entirely eliminated. Furthermore, pyrotechnic articlesmade by the invention method have demonstrated their efliciency andreliability over extended trial periods. As a result, and in view oftheir lower cost and ease of fabrication, they have largely replacedcombustible flares and fuses made in the conventional manner.

Obviously certain modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claim the invention maybe practiced otherwise than as specifically described.

We claim:

A consumable pyrotechnic mixture consisting of essentially equal partsby weight of a fuel and a resinous composition, the former consisting ofapproximately one part by weight of atomized magnesium powder andapproximately two parts by weight of potassium perchlorate, the latterconsisting of between one and ten percent by weight of benzyl alcohol,less than ten percent by weight of cobalt naphthenate, between one-halfand six percent by weight of methyl ethyl ketone peroxide, and theremainder of a mixture of two unsaturated polyester resins each havingstyrene as a reactive monomer, one of said two resins being derived frompropylene glycol, maleic anhydride and phthalic anhydride, the ratio ofmaleic anhydride to phthalic anhydride being relatively high, the otherof said two resins being of the flexible type based upon diethyleneglycol, maleic anhydride and adipic acid, the said resin mixture beingcharacterized by its ability to remain in a solid state while the saidpyrotechnic mixture is being consumed.

References Cited in the file of this patent UNITED STATES PATENTS613,021 Schwartz Oct. 25, 1898 1,756,255 Meek Apr. 29, 1930 2,407,131Brunson et a1. Sept. 3, 1946 2,410,801 Audrieth Nov. 12, 1946 2,557,667Kropa June 19, 1951 2,700,603 Hart et a1 Ian. 25, 1955 FOREIGN PATENTS580,409 Great Britain Sept. 6, 1946

